Survival analysis of rutting failures in hot in-place recycling maintained asphalt pavements using field data

Reclaimed asphalt pavement (RAP) serves as an eco-friendly alternative to new construction materials. Hot In-Place Recycling (HIR), which involves the complete on-site recycling of RAP, emerges as a sustainable maintenance solution with resource conservation and cost reduction benefits. Numerous laboratory studies have delved into its advantages, focusing on aspects such as the rejuvenation of binding agents and improved resistance to rutting. Despite its performance benefits, research into extending pavement service life via this technology is limited due to a lack of comprehensive maintenance history and performance inspection data, i.e., censored data. To address this, survival analysis, a method commonly used in the medical field to evaluate treatment effectiveness, was applied. Specifically, a multistate survival analysis, incorporating the non-parametric Kaplan-Meier (KM) method, semi-parametric Cox proportional hazards regression model (Cox regression model) and a parametric generalized F model, was conducted. The treatment service life (TSL) was introduced to measure the duration between the completion of one maintenance activity and the occurrence of the next. The analysis of data from the Jiangsu Provincial Maintenance Management System revealed several noteworthy insights. For instance, a 1 mm increase in the initial rutting depth (RD) raised the risk of re-maintenance for HIR-treated segments by a factor of 1.03. Additionally, delaying maintenance by one year resulted in a 27% increase in the risk of re-maintenance, and a 1,000-fold rise in Equivalent Single Axle Load (ESAL) doubled the risk of re-maintenance. The median TSL for HIR-maintained sections, as estimated through the Generalized F model, was approximately 8.87 years, closely aligned with the median TSL of 9 years obtained using the KM method and the Cox regression model. This approach adeptly addresses the crucial challenge of determining the optimal timing and choosing effective maintenance treatments for pavements, a pivotal element of sustainable maintenance management. These findings disrupt the traditional belief that HIR is predominantly cost-effective without delivering significant long-term improvements in pavement performance. Instead, they emphasize the potential of HIR as a sustainable pavement maintenance treatment, advocating for its widespread adoption and implementation in pavement maintenance.